      (typical-density density-unit substance)))
   ([density-unit substance]
    (condp = density-unit
-     :lb-per-cu-ft (let [[density _ substance] (typical-density :kg-per-m3)]
-                     [((convert-units-f :kg-per-m3 :lb-per-cu-ft) density) :lb-per-cu-ft substance])
-     :kg-per-m3    (condp = substance
-                     ;; Typical values for different substances taken from
-                     ;; https://serc.carleton.edu/mathyouneed/density/index.html#:~:text=Typical%20densities%20for%20gasses%20are,or%207%20g%2Fcm3.
-                     ;; accessed on 23-Dec-2020. Additionally, the data for metals was taken from
-                     ;; https://theengineeringmindset.com/density-of-metals/ accessed on 23-Dec-2020.
-                     (let [density (condp = substance
-                                     :gas    (tuc/draw-normal 1 0.11)
-                                     :liquid (tuc/draw-normal 1000 110)
-                                     :rock   (tuc/draw-normal 3000 330)
-                                     :metal  (tuc/draw-normal) 10355 5431)]
-                       [density density-unit substance])))))
+     :lb-per-cu-ft (density-as (typical-density :kg-per-m3 substance) :lb-per-cu-ft)
+     :kg-per-m3 (let [density (condp = substance
+                                ;; Typical values for different substances taken from
+                                ;; https://serc.carleton.edu/mathyouneed/density/index.html#:~:text=Typical%20densities%20for%20gasses%20are,or%207%20g%2Fcm3.
+                                ;; accessed on 23-Dec-2020. Additionally, the data for metals was taken from
+                                ;; https://theengineeringmindset.com/density-of-metals/ accessed on 23-Dec-2020.
+                                :gas    (tuc/draw-normal 1 0.11)
+                                :liquid (tuc/draw-normal 1000 110)
+                                :rock   (tuc/draw-normal 3000 330)
+                                :metal  (tuc/draw-normal) 10355 5431)]
+                  (make-measurement density density-unit substance)))))
 
 (defn typical-total-pump-energy
   ([]

        measurement (generate-measurement-f unit)]
    [measurement (measurement-as-f measurement (first (remove (partial = unit) units)))]))

(generate-measurement-pair #{:lb-per-gal :kg-per-m3}
                           rand-proppant-concentration-unit
                           typical-proppant-concentration
                           proppant-concentration-as)

   ;; Retrieved from http://www.excoresources.com/appalachia/ and
   ;; https://en.wikipedia.org/wiki/Casing_string on 28-Dec-2020.
   (let [typical-casing-outer-diameter-inches (+ 5 (/ 1 2))
         typical-casing-pipe-width-inches 0.545
         typical-casing-inner-diameter-inches (- typical-casing-outer-diameter-inches
                                                 typical-casing-pipe-width-inches)
         typical-casing-area-sq-inches (* 2 Math/PI (/ typical-casing-inner-diameter-inches 2))
         typical-pressure-psi (magnitude (typical-surface-treating-pressure :psi))
         typical-force-lbf (* typical-pressure-psi typical-casing-area-sq-inches)]
     (condp = force-unit
       :lbf (make-measurement typical-force-lbf force-unit)
       :N   (force-as (typical-force :lbf) :N)))))
